Status of the invasive wasp species, Vespula germanica and Polistes dominula in South Africa, and the feasibility of various management strategies

Thesis (PhDAgric)--Stellenbosch University, 2016.ENGLISH ABSTRACT: The main objective of this study was to determine the current status of two invasive wasps, Vespula germanica and Polistes dominula, in South Africa and to explore the feasibility of implementing various management strategies to control and/or eradicate them. Both wasp species pose a potential threat to biodiversity and agriculture in the Cape Floristic Region (CFR), as well as being a nuisance to people. In an effort to identify suitable biocontrol agents, the pathogenicity of three likely indigenous entomopathogenic nematode (EPN) species and one likely indigenous entomopathogenic fungal (EPF) species was tested against both V. germanica and P. dominula larvae in a bioassay trial. The three EPN species were Heterorhabditis bacteriophora,H. noenieputensis and Steinernema yirgalemense. The fungal species tested was Beauveria bassiana. Both V. germanica and P. dominula larvae were highly susceptible to all of the biocontrol agents tested, and died of infection within 4 days after inoculation within EPN and within 7 days after innoculation within the EPF. The EPN Heterorhabditis bacteriophora which performed best in the bioassay trial, as well as the EPF, Beauveria bassiana, were then tested in the field to determine its ability to infect P. dominula larvae by spraying inoculum directly onto nests. Four treatments were applied, namely: an aqueous solution of the EPF, an aqueous solution of the EPN, a mixture of the EPF and EPN species, and a control of distilled water. The combination of EPF and EPN caused the highest mortality in both P. dominula larvae (31.39 %) and pupae (3.42 %) compared to the other treatments, but infection levels were much lower than those obtained under laboratory conditions. An unsuspected discovery was made, when it appeared that 13 % of all nests used in this trial were parasitized by an unclassified fly species, identified to be a species from the Tachinidae family. There was no significant difference between the ability of fly larvae that were treated with the control, to develop into adults over a period of 144 h, compared to those treated with the various biocontrol agents. Landmark-based geometric morphometric analyses were used to identify the potential origin of introduced V. germanica wasps and to determine the possible route of invasion followed in South Africa. Variation in forewing shape among wasp worker samples that were collected from five different countries, including South Africa, Australia, New Zealand, Argentina and France, was compared. An overall direct correlation between the wing shape and the geographic distance between two sites was found. This result suggests that the morphological variation in wasps from South Africa can be explained as isolation-by-distance. Results inferred that wasps had spread from Kirstenbosch to Somerset West, and thence through Stellenbosch to Franschhoek. The wing shape of wasps collected from Kirstenbosch, the area where the first V. germanica specimen was found, mostly resembled the wing shape of samples from France, compared to all the other overseas localities. Therefore, one could conclude V. germanica wasps were most likely transported from Europe to South Africa. The attractiveness of a range of lures and baits to V. germanica and P. dominula females collected in the field were tested using a Y-tube olfactometer. A combination of protein and carbohydrate-based baits were tested. Vespula germanica mostly preferred cooked ham, whereas P. dominula was mostly attracted to the odours emanating from their own nest.AFRIKAANSE OPSOMMING: Die hoofoogmerk van hierdie studie was om die huidige status van twee indringerwespe, Vespula germanica en Polistes dominula, in Suid-Afrika te bepaal, en om die raadsaamheid te ondersoek om bestuurstrategieë toe te pas om die wespe te beheer. Albei spesies wespe hou ‘n potensiële bedreiging in vir biodiversiteit en landbou in die Kaapse Floristiese Streek (KFS), en hulle is ‘n ergernis vir mense. Ten einde geskikte agente vir biokontrole te identifiseer, is die patogenesiteit van drie spesies waarskynlik inheemse entomopatogeniese nematode (EPN) en een spesie waarskynlik inheemse entomopatogeniese fungus (EPF) getoets in ‘n bio-essaiproef op die larwes van sowel V. germanica as P. dominula. Die EPN spesies was Heterorhabditis bacteriophora, H. noenieputensis en Steinernema yirgalemense, en die fungusspesie Beauveria bassiana. Die larwes van sowel V. germanica as P. dominula was hoogs watbaar vir al die biokontrole-agenta in die proef, en het binne 4 dae na inenting met die EPN en binne 7 dae na inenting met die EPF, van infeksie gesterf. Die EPN Heterorhabditis bacteriophora, wat die beste in die bio-essaiproef gevaar het, sowel as die EPF, Beauveria bassiana, is daarop in die veld getoets deur entstof regstreeks op die neste te spuit om hul vermoë te bepaal om die larwes van P. dominula te infekteer. Vier behandelings is toegedien, naamlik: ‘n water-oplossing van die EPF, ‘n water-oplossing van die EPN, ‘n mengsel van die EPF- en EPN-spesies, en ‘n kontrole van gedistilleerde water. Die kombinasie van EPF en EPN het die hoogste sterfte veroorsaak in sowel P. dominula se larwes (31.39 %) as papies (3.42 %) in vergelyking met die ander behandelings, maar die vlakke van infeksie was heelwat laer as wat onder laboratoriumtoestande verkry is. ‘n Onverwagte ontdekking is gedoen, toe dit blyk dat 13 % van alle neste wat in hierdie proef gebruik is deur ‘n ongeklassifiseerde vlieg-spesie, van die familie Tachinidae, geparasitiseer is. Daar was geen noemenswaardige verskil tussen die vermoë van vlieglarwes wat behandel is met die kontrole en dié behandel met die onderskeie biokontrole-agente, om in volwassenes te ontwikkel oor ‘n tydperk van 144 h nie. Ten einde die moontlike oorsprong te bepaal van ingevoerde V. germanica wespe, asook die moontlike roete van indringing wat in Suid-Afrika gevolg is, is oriëntasiepunt-gegronde geometriese morfometriese analises gedoen. Verskille in die vorm van voorvlerke is vergelyk tussen voorbeelde van werkerwespe wat in vyf verskillende lande versamel is, waaronder Suid-Afrika, Australië, Nieu-Seeland, Argentinië en Frankryk. ‘n Algehele regstreekse korrelasie is gevind tussen die vlerkvorm en die geografiese afstand tussen twee plekke. Hierdie resultaat dui daarop dat morfologiese afwykings tussen wespe in Suid-Afrika verklaar kan word as isolasie-deur-afstand. Uit die resultate kan afgelei word dat die wespe van Kirstenbosch na Somerset-Wes versprei het, en vandaar deur Stellenbosch na Franschhoek. Die vlerkvorm van wespe wat in Kirstenbosch versamel is, die gebied waar die eerste V. germanica voorbeeld gevind is, het in vergelyking met die ander oorsese plekke, die meeste soos die vlerkvorme van voorbeelde uit Frankryk gelyk. Die gevolgtrekking kan dus gemaak word dat V. germanica wespe heelwaarskynlik van Europa na Suid-Afrika vervoer is. Die aantreklikheid van ‘n reeks lokmiddels en aas vir V. germanica en P. dominula wyfies wat in die veld versamel is, is in ‘n Y-buisolfaktometer getoets. ‘n Kombinasie van aas met ‘n proteïen- of koolhidraatbasis is getoets. V. germanica het gekookte ham die meeste verkies, terwyl P. dominula meestal gelok is deur die geure vanuit hul eie nes